(1) Field of the Invention
The present invention relates to a gas heat exchange apparatus for effecting heat exchange, especially sensible heat exchange, in a plurality gas streams, for example, a cross flow heat exchanger or a rotary regenerative heat exchanger. More particularly, the present invention relates to a heat exchange element for use in this heat exchange apparatus and a process for the preparation of this heat exchange element.
(2) Description of the Related Art
Gas heat exchange elements formed by preparing a sheet from an organic fiber or inorganic fiber as the main starting material and processing the sheet to a honeycomb structure member are known, as disclosed in Japanese Patent Application Laid-Open Specifications No. 127663/77 and No. 19548/79. Heat exchange elements of this type are advantageous over heat exchange elements having a similar honeycomb structure, which are obtained by extrusion molding of ceramic materials, in that the weight is light, an element having a large size can be prepared and the productivity is high. Accordingly, heat exchange elements of this type have been practically used for cross flow heat exchangers and rotary regenerative heat exchangers or in other fields.
According to the intended use, gas heat exchanger elements are roughly divided into an element for exchange of sensible heat, an element of exchange of latent heat (dehumidification or reduction of the humidity) and an element for exchange of total heat (sensible heat and latent heat). In elements for exchange of latent heat and exchange of total heat, a moisture-absorbing agent such as lithium chloride, lithium bromide or a molecular sieve is supported on a sheet material.
In a gas heat exchange element formed by processing a sheet material (hereinafter referred to as "heat exchange element"), the properties required in addition to the heat exchange capacity are a durability under severe conditions, to which a sensible heat exchange element is exposed, and a gas-intercepting property.
More specifically, when the heat exchange element is used as a sensible heat exchange element, if a gas containing, for example, an oxide of sulfur is treated in a low-medium temperature region, the sulfur oxide is condensed and adheres to and permeates into the heat exchange element. Accordingly, the heat exchange element cannot be used for a long time because of early deterioration of physical properties unless the heat exchange element has not only a heat resistance but also an acid resistance.
Furthermore, it is desired that a sheet material constituting an element of a cross flow heat exchanger or rotary regenerative heat exchanger having a honeycomb-shaped fluid passage will not allow permeation of a gas and will have a good gas-intercepting property so that mingling of gases is not caused in the portion acting as a partition wall for two gases, between which heat exchange is effected.
In many cases, the required acid resistance can be attained if the sheet constituting the heat exchange element is wholly composed of a material having a good acid resistance. Furthermore, the gas-intercepting property can be improved by increasing the pack density or coated amount of an inorganic filler used for the sheet material. However, it is very difficult to simultaneously attain a high acid resistance and a high gas-intercepting property in a heat exchange element composed of a sheet material without degradation of light weight and thin thickness characteristics of the sheet material. Accordingly, even in conventional heat exchange elements having a relatively good gas-intercepting property, the level of this gas-intercepting property is still very low.